Osteoarthritis (OA) is a degenerative disease characterized by gradual loss of articular cartilage. The etiology of OA is unknown, but repetitive mechanical injury, including abnormal joint anatomy, appears to play a central role. Other factors are involved, however, including genetic and biochemical factors affecting cartilage chondrocytes.
Cytokines, essential mediators of cell growth and regulation, are also involved in the pathogenesis of OA. For example, IL-1, TNF, IL-6, IL-18, LIF and OSM may be found in OA joint fluids and tissues, and these cytokines have significant catabolic effects on chondrocytes.

The figure shows the involvement of some of these cytokines, and of cartilage-degrading proteinases, in processes leading to OA.